1. Field of the Invention
The present invention relates to drive systems.
2. Description of the Related Art
In general, torque fluctuations also lead to fluctuations in rotary speed. Both the torque fluctuations and the rotary speed fluctuations affect the motor vehicle and its driving performance in various ways. In particular, these fluctuations cause an impairment of driving safety, driving comfort, and wear on parts, or they necessitate a larger dimensioning of these parts because of the heightened vulnerability to wear and tear of parts under fluctuating strain.
Specifically, the impairment of driving safety results from the fact that rotary speed fluctuations in the drive train result in fluctuations in the vehicle""s velocity. These velocity fluctuations lead to xe2x80x9cbuckingxe2x80x9d (longitudinal accelerations and decelerations) of the vehicle. Torque fluctuations can lead to pitching of the vehicle about its transverse axis. Both effects can impair the track stability of the vehicle as a result of the forces and moments associated with the fluctuations. In particular, these effects, and especially the velocity fluctuations, can lead to slippage between the driving wheels and the roadway (drive slip) and, thus, prevent safe steering.
Many drivers have a tendency to xe2x80x9ctake their foot off the gasxe2x80x9d when negotiating a curve, i.e., to throttle or intercept the fuel supply; the driver thinks that velocity reduction makes it safer to negotiate the curve. But such a load change often results in drive slip as well. Tracking may be lost, and the vehicle is pulled tangentially out of the curve. Thus, by throttling or interrupting the fuel supply, the driver has created a dangerous situationxe2x80x94instead of placing the vehicle in a safer condition.
Most passengers perceive the effects of xe2x80x9cbucking,xe2x80x9d xe2x80x9crockingxe2x80x9d and xe2x80x9cpitchingxe2x80x9d of the vehicle as a disturbance and, thus, as impairing the driving comfort.
The ongoing stressing of parts with changing forces and torques leads to premature material fatigue, e.g., fatigue fracture. This is a disadvantage, since premature wear not only produces higher repair costs, but also detracts from the overall vehicle reliability. Moreover, failure of parts in the drive region and drive trainxe2x80x94because of the generally associated failure of the overall drivexe2x80x94is a safety risk, especially in critical driving situations, such as passing or entering a heavy traffic intersection.
Finally, the wear associated with such torque fluctuations requires a larger dimensioning of various parts in the drive system or drive train. Not only does this make the vehicle more expensive, it also increases its weight. And heavier weight is a disadvantage, due to greater fuel consumption.
In the state of the art, it is known how to counteract load change oscillations by controlling the internal combustion engine such that the load change transition (the transition from one torque level to another) is more gentle. But since the control of the internal combustion engine is relatively imprecise and sluggish, and the size of the moments of the engine is limited and thus often not sufficient, this method of reducing torque fluctuations by controlling the engine is only of limited use.
The invention concerns a drive system with a drive engine, in particular, an internal combustion engine of a motor vehicle, and a drive train. Moreover, the invention concerns an electric machine for use in such a drive system. Furthermore, the invention concerns a method for operating such a machine in such a drive system.
In motor vehicles, various torque fluctuations occur in the drive trainxe2x80x94including, in particular, drive transmission, articulated and axle shafts and also in part crankshafts. Such torque fluctuations occur when the torque put out by a drive engine of the motor vehicle is superimposed on another torque. This additional torque arises from the drive system of the motor vehicle itself and/or arrives from the outside in the drive system. Accordingly, there is a resultant torque in the drive train, which is often subject to so-called drive train torque fluctuations. One example of a torque arising from the drive system itself are load alternation oscillations (periodic fluctuations of the torque due to a load change); an example of torques arriving in the drive system from the outside are torques which get into the drive system through effects on a drive wheel, for example, when the vehicle is traveling on a rough roadway.
By fluctuation is meant, in connection with the invention, a deviation from a mean value. This includes both periodic and nonperiodic, in particular, onetime deviations.
An improved drive system and method of operating the improved drive system with the improved drive system comprising at least one drive motor such as an internal combustion engine of a motor vehicle, and a drive train (27), at least one electric machine (26), which can apply a braking and/or driving torque to the drive motor (1) and/or drive train (27) and/or form a coupling in the drive train (27); and at least one open-loop/closed-loop control system, which controls/regulates the electric machine (26) such that it diminishes the drive train torque and/or speed fluctuations.